Atomic Modulation Triggering Improved Performance of MoO₃ Nanobelts for Fiber-Shaped Supercapacitors

Asymmetric supercapacitors (ASCs) are emerging as a new class of energy storage devices that could potentially meet the increasing power and energy demand for next-generation portable and flexible electronics. Yet, the energy density of ASC is severely limited by the low capacitance of the anode side, which commonly uses the carbon-based nanomaterials. Here, the demonstration of sulfur-doped MoO_{3- x} nanobelts (denoted as S-MoO_{3- x} ) as the anode for high-performance fiber-shaped ASC are reported. The Mo sites in MoO₃ are intentionally modulated at the atomic level through sulfur doping, where sulfur could be introduced into the MoO₆ octahedron to intrinsically tune the covalency character of bonds around Mo sites and thus boost the charge storage kinetics of S-MoO_{3- x} . Moreover, the oxygen defects are occurring along with sulfur-doping in MoO₃ , enabling efficient electron transport. As expected, the fiber-shaped S-MoO_{3- x} achieves outstanding capacitance with good rate capability and long cycling life. More impressively, the fiber-shaped ASC based on S-MoO_{3- x} anode delivers extremely high volumetric capacitance of 6.19 F cm^-3 at 0.5 mA cm^-1 , which makes it promising as one of the most attractive candidates of anode materials for high-performance fiber-shaped ASCs.